Introduction: Arduino Smart Dryer

This project uses Arduino Uno to build an automatic dryer which only activates when the paper, towel or piece of cloth (connected to probes) is wet to a certain degree. As the amount of water in the target material changes, the corresponding resistance changes, and based on that Arduino turns on or off the fans. In other words, based on how "wet" the cloth is, you can program the Arduino to turn on and dry the material. This could also be applied to a fresh paint on a surface. This is a good informative project for people who want to start working with Arduino Uno, to learn about transistors and motors, as well as RC time concept (to measure changing resistance). Now...let's make a smart dryer together!

Step 1: Parts

To build the automatic dryer you need these parts:

Arduino uno

2 Resistors (1kΩ and 220Ω)

NPN Transistor

Capacitor (I used 0.047 uF here but anything up to 1uF is fine)

(1 or 2) 3.7V Motors with Helicopter Propellers (any small DC motor would do the job)

Battery pack (AA batteries)

Jumper Wires


Long matches (wood sticks)


A piece of foam board

LED (Optional)

Step 2: Building a Frame for Fans and Arduino

We will need to fix the fan(s) in a position facing the wet paper/towel. To make that easier and the device fancier (:D), let’s make a wooden frame. After gluing wooden sticks, add a piece of foamboard, make two holes in it, and fix the motors inside.

Step 3: Wiring Up

I have made a sketch for the circuit which should make your job easier at this step! Please follow the sketch and have in mind that some of them are for presentation (for example, as mentioned before, I used a ceramic capacitor of .047 uF which is different than the capacitor shown in the sketch). Also, I connected a 1Kohm resistor to the middle leg of transistor, and 150 ohm ones are used on the other half of breadboard.

Step 4: Arduino Codes (sketches)

I’m providing you with two sketches, one for calibration and one for the main job. To read more, the following are two tutorials from Arduino official website related to this project:

Capacitance Meter Tutorial

RCTime Tutorial

Step 5: Calibration

As you can see in the calibration code, the resistance values are printed on the serial monitor. Based on these value and after several trial and errors with dry/wet napkins (for example) you can set a threshold value for the fans to start working.

Step 6: YOU Did It!!!

Awesome! I knew you could build it!! Just note that for any material you should do the calibration step again, to figure out the threshold value for the changing resistance of that material based on how wet or dry it is. Thanks!